Particle sorting, selecting, and manipulation apparati have been designed for a number of applications. Depending on the particles, the underlying mechanisms of different sorting devices may offer certain advantages to others. For example, biological particles (such as cells) are one type of particle that may have particular requirements for sorting, selecting, manipulation, and analysis.
Hydrodynamic pressure control, electrokinetics, and radiation pressure are three common approaches used in current particle/cell sorting systems. In particular, laser trapping and guiding by photon pressure is a known technique for sorting particles. A radiation pressure based cell sorting mechanism is generally preferred due to less induced cell stress and disturbance, along with a simple means for integration.
A radiation pressure based cell sorting device was disclosed in U.S. Pat. No. 4,887,721 to Martin et al. This patent describes using photon pressure to propel particles along paths predefined by laser beams. The setup involves a probing laser beam to characterize the optical property of particles and a deflection beam to propel the selected objects. Unfortunately, the system uses free space optics and its components are bulky and difficult to package into an integrated device. As well, the system is only suitable for considerably large objects (greater than 1 mm), and the length scale of the instrument is on the order of millimeters.
U.S. Pat. No. 7,068,874 to Wang et al. also describes a cell sorting device using microfluidic systems molded in PDMS clear plastic. In this approach, a laser beam of Laguerre-Gaussian profile, emanating from Vertical Cavity Surface Emitting Laser (VCSEL) is launched in free space from the top of the device. By moving around the PDMS microfluidic device on a micromanipulation stage, one can effectively manipulate the particles on the plastic chip. This setup, however, relies on sophisticated free space optics for laser beam collimating, shaping and focusing to achieve desired intensity structure in order to produce effective laser tweezing, making it very difficult to integrate to form a complete and self-contained apparatus for cell manipulation purposes.
Various techniques of fabricating waveguides in semiconductor and transparent material have been developed.
For example, U.S. Pat. No. 7,116,878 describes a waveguide structure that consists of a core layer, a cladding layer, and a buffer layer in which optical signals can be confined and manipulated.
As well, U.S. Pat. No. 7,120,325 teaches a 2D optical waveguide that comprises light transmitting and receiving units to enable monolithic integration of optical transmission. These devices, however, are not suitable for biological application and are difficult to interconnect with microfluidic systems.
A UV embossing technique was disclosed in U.S. Pat. No. 6,341,190, in which waveguiding structures can be made onto plastic films or glass, silicon substrates. The process, however, is tedious, and difficult to interconnect with microfluidic networks on a single platform.
In view of the foregoing, what is needed are systems and methods for manipulating particles using waveguides that are simple and effective, and overcome the disadvantages and limitations of current techniques.